A conventional umbrella as shown in FIG. 1 includes: a rib means 2 having a top rib 21 pivotally secured to an upper notch 11 fixed on an upper portion of a central shaft 1, a stretcher rib 22 pivotally secured to a runner 12 slidably held on the central shaft 1, whereby upon opening of the umbrella, a bottom periphery 121 of the runner 12 will be retained on an upper spring catch 13 resiliently protruding externally through an upper slot 131 cut in the central shaft; and upon closing of the umbrella (as shown in dotted lines of FIG. 1), a lower spring catch 14 as resiliently protruding externally on the central shaft 1 through a lower slot 141 cut in the shaft 1 will engage a runner slot 122 cut in the runner 12 for locking the runner 12 and the rib means 2 at a folded or closed state.
However, such a conventional umbrella will have the following drawbacks:
1. For cutting the slots 131, 141 for resiliently holding the spring catches 13, 14 in the central shaft 1, a strength of the shaft 1 will be greatly reduced, causing deformation of the shaft and influencing the opening and closing operation of the umbrella.
2. The spring catch 13, 14 is made of thin metal plate and will easily cause injury to an umbrella user when depressing the catch 13, 14 inwardly for opening or closing the umbrella.
3. If the central shaft 1 is made of metalic materials, a serious corrosion will occur at the slots 131, 141 especially after being penetrated with raindrops therein in a rainy days to easily damage the umbrella.
4. The contact area between the catch and the runner is limited to a "single spot" to easily cause wearing between the catch and the runner, possibly influencing a smooth operation of the umbrella. Meanwhile, a poor quality control for making the umbrella, such as unprecise installing of the catch in the shaft or a misalignment between the catch 14 and the runner slot 122 cut in the runner 12, may even deteriorate the umbrella.
The present inventor has found the drawbacks of the conventional umbrella, and invented the present invention by eliminating any spring positioning means externally extended on the shaft.